As a capacitor which contains an electrolytic solution inside of its exterior case, there are an electrolytic capacitor and an electric double-layer capacitor.
In the electrolytic capacitor, metal referred to as a valve metal such as aluminum, tantalum and niobium is used for its electrodes, an anode of the electrodes is oxidized, and the resultant which is an oxide film layer is used as a dielectric.
In the electric double-layer capacitor, a phenomenon (an electric double-layer) in which charges are arrayed at extremely short distances in interfaces between electrodes (polarized electrodes) and an electrolytic solution is utilized.
In a method of manufacturing an aluminum electrolytic capacitor in which aluminum is used for its electrodes, etching processing and oxide film formation processing are performed, an anode foil and a cathode foil to which electrode lead-out terminals are respectively attached are wound via separators, and the resultant is fixed by an element stopper tape, thereby forming a capacitor element. This capacitor element is impregnated with an electrolytic solution for driving and thereafter, is housed in an exterior case having a cylindrical shape with a bottom. There may be a case where the capacitor element is fixed inside of the case by using a fixation material.
Further, an opening sealing body is attached to an opening of the exterior case, and the opening has a configuration which is sealed through drawing processing.
In an aluminum electrolytic capacitor whose terminal shape is substrate-self-supporting-type, a positive electrode terminal and a negative electrode terminal are formed on an external end face of the opening sealing body, and a positive electrode tab terminal and a negative electrode tab terminal led out from the capacitor element are electrically connected to end portions of these terminals. In addition, in an aluminum electrolytic capacitor whose terminal shape is lead-wire type, lead terminals electrically connected to a positive electrode tab terminal and a negative electrode tab terminal which are led out from a capacitor element are led out externally through an insertion hole provided in an opening sealing body.
A capacitor element of the electric double-layer capacitor in which polarized electrode layers are formed on current collectors formed of a metal foil such as an aluminum foil is obtained by winding an anode foil and a cathode foil to which electrode lead-out terminals are attached via separators. In the electric double-layer capacitor, the capacitor element mentioned above is impregnated with an electrolytic solution and is housed in a case formed of aluminum or the like and having a cylindrical shape with a bottom. As described above, the electric double-layer capacitor and the aluminum electrolytic capacitor are different from each other only in configurations of the electrodes and have the same configurations.
When an abnormal stress such as an overvoltage and an excessive ripple current is applied to each of the above-described capacitors containing the electrolytic solution thereinside, the electrolytic solution is decomposed and a gas is generated. When this generation of the gas increases an internal pressure of the capacitor, the capacitor is ruptured. Therefore, a weak portion is provided at a bottom portion of the exterior case having the cylindrical shape with the bottom and is caused to function as a safety device (pressure valve) operating in accordance with an increase in the internal pressure to release the internal pressure externally.
A pressure at which this pressure valve operates can be set to a desired pressure by adjusting a thickness of the weak portion. However, the higher the pressure at which the pressure valve operates is, the larger a range in which the valve is opened is, thereby leading to a problem in that the bottom portion of the exterior case after opening the valve is largely deformed. Therefore, there proposed is the technology in which a thick-wall portion formed so as to be thicker than a side wall portion is formed in a bottom of the exterior case, a thin-wall portion is formed within a range of this thick-wall portion, and linear grooves serving as the weak portion are further formed in the thin-wall portion, thereby limiting to the thin-wall portion the range in which the valve is opened (refer to Patent Literature 1).